The invention relates to a process for improving the moldability of expandable styrene polymer particles having reduced flammability.
Polymer foams are highly desirable in building construction because of their light weight and good heat insulating property. A prerequisite for use in the construction industry is the foam must have reduced flammability. Many halogenated organic compounds have been proposed as additives for the purpose of reducing the flammability of the foams.
In the case of expandable styrene polymer particles, the non-polymeric halogen compounds are often added to the particles by heating an aqueous suspension of styrene polymer particles in the presence of the halogen compound and a blowing agent until the particles are impregnated with the additives. Impregnation with the blowing agent to produce expandable styrene polymer particles may be carried out at temperatures between 60.degree. and 150.degree. C. However, when the organic halogen compounds are added to the impregnation system, lower temperatures, usually 60.degree.-90.degree. C., are used to prevent decomposition of the halogen compound which may in turn cause degradation of the polymer and subsequent impairment of the expanding and molding properties of the polymer. These lower temperatures require longer time for the impregnation process and, in the case of larger polymer particles, the particles may not be completely impregnated, as shown by the presence of hard cores in the particles after expansion. Shorter times of impregnation and the elimination of hard cores in the particles can both be accomplished by carrying out the impregnation at temperatures higher than 100.degree. C.
Particles impregnated at these higher temperatures may exhibit molding properties which are inferior to the properties of particles prepared at the lower temperatures. Thus, the particles may produce prepuff having a surface skin, i.e., denser foam at the surface and lighter foam at the cores and exhibit increased "pruning" (i.e. a nonspherical shape due to large internal cells). The pre-puff may also contain water occluded from the suspension. On molding, these pre-puff particles exhibit reduced fusion and poor dimensional stability.